When ions are accelerated by an electric field, ions having smaller masses are more easily accelerated, while ions having greater masses are less easily accelerated. A time-of-flight (TOF) mass spectrometer is an instrument for performing mass analysis by measuring the differences in flight time (i.e., the time taken for ions to reach the ion detector) by making use of the principle described above.
In a TOF mass spectrometer, as the ion flight distance increases, ion mass differences tend to produce greater flight time differences. Therefore, one method of improving the resolution of the instrument is to increase the flight distance.
One known method for achieving both increase of flight distance and miniaturization of the instrument is to cause the direction of flight of ions to make a U-turn, using electric fields, for example.